Crisis in Ukraine: What you need to know

The United States escalated its response to Russia’s military and economic threats to Ukraine on Thursday, announcing it has imposed visa bans on officials and others deemed responsible for actions that have undermined Ukraine’s sovereignty and territorial integrity. The announcement came as the European Union was considering its own punitive measures and as Secretary of State John Kerry met for a second day with the Russian foreign minister, Sergey V. Lavrov, on ways to defuse the Ukraine crisis, one of the most serious East-West confrontations since the Cold War.

The situation in Ukraine became tense on March 3 after Russian President Vladimir Putin received approval from his country's parliament to send troops into Crimea over the weekend.

Catch up with the latest developments in Ukraine's violent and tense situation.

On Feb. 21, Ukrainian President Viktor Yanukovych, opposition leaders and representatives of the European Union signed a deal to end the country's bloody political crisis that has left parts of Kiev's city center a war zone.

The next day, Ukraine's parliament voted unanimously to remove President Viktor Yanukovych from office and hold early elections on May 25.

Yanukovych took to television airwaves later in the evening, saying he had been forced to leave Kiev because of "vandalism, crime and a coup." "I don't plan to leave the country. I don't plan to resign. I am the legitimate president," he said in an interview from Kharkiv, a pro-Russian stronghold near Ukraine's border with that nation.

But according to the head of Ukraine's Border Guard Service, Yanukovych and his entourage attempted to board a charter flight without proper documentation in the eastern city of Donetsk. He was on the tarmac when he was turned back by security forces. As of Sunday, no one seemed to know exactly where Yanukovych was.

On the same day parliament voted to oust Yanukovych, former Prime Minister Yulia Tymoshenko, who is one of Yanukovych's political rivals, was freed after 2½ years in prison and returned to the capital, where she declared Ukraine was done with the "terrible dictator" Yanukovych.

Tymoshenko served as prime minister from 2007 until she was forced out of office in 2010 after losing an election to Yanukovych. A year later, she was sentenced to seven years in prison after being convicted of abuse of authority over a natural gas deal negotiated with Russia. The West considers her case politically motivated and has called her a political prisoner.

On Feb. 22, Oleksandr Turchinov, the speaker of Ukraine's parliament, took on the duties of ousted President Viktor Yanukovych. The appointment became official after the parliamentary vote was published in the government gazette. Also Sunday, lawmakers fired Foreign Minister Leonid Kozhara and Education Minister Dmytro Tabachnik.

Also on Feb. 22, Oleksandr Yefremov, parliamentary leader of Yanukovyc's party, condemned Ukraine's ousted president in a video statement, blaming him for the "robbery and deception" of the nation. The former ruling party blamed Yanukovych for illegal orders that led to casualties, financial debt and shame in the eyes of the world, Yefremov said.

On Feb. 23, an arrest warrant was issued for Yanukovych, said acting Ukrainian Interior Minister Arsen Avakov. "As of this morning, a criminal case on mass killings of civilians has been opened. Yanukovych and several other officials have been placed on the wanted list," he wrote on his Facebook page, as reported by Russian news agency Interfax.

Ousted Ukrainian President Viktor Yanukovych remained defiant in a press conference on Feb. 28, insisting that he remains the country's legitimate elected leader and will not give up power.

On Feb. 27, pro-Russian gunmen seized several government buildings in the Crimean capital of Simferopol. On Feb. 28, mysterious troops appeared outside airports in Crimea.

On March 1, the Russian parliament gave President Vladimir Putin authority to send troops to Ukraine. Russian forces began flooding the peninsula.

Tension pervaded the capital city March 3 as residents awaited Russia's next move. Ukraine's political leaders appealed to world powers to help stop Russia and vowed to stand up to any further Russian moves. "Nobody will give Crimea away," interim Prime Minister Arseniy Yatsenyuk said. "There are no grounds for the use of force against civilians and Ukrainians, and for the entry of the Russian military contingent."

Also on March 3, Moscow denied a report in Russian state media claiming it had issued an ultimatum to Ukrainian forces to clear out of Crimea by Tuesday morning or face a "military storm." Meanwhile, Foreign Minister Sergey Lavrov brushed aside claims that Russia's troop movements were an act of aggression. "I repeat: This is a matter of defending our citizens and our compatriots, of defending the most important human right -- the right to life," he said.

Before the violence during the initial protests stopped on Feb. 21, at least 25 people were killed in the protests, including police officers.

Thousands of demonstrators have packed Independence Square since November, when President Viktor Yanukovych reversed a decision to sign a trade deal with the European Union and instead turned toward Russia.

A view shows clashes at Independence Square in Kiev early in the morning of Feb. 19, 2014.